Patent Literature 1 (Japanese Patent Application Laid-open Publication No. 2009-276747) discloses a wavelength selective switch to be used in a wavelength division multiplex system. This wavelength selective switch has a plurality of fiber ports arranged in a fiber port array and a plurality of optical elements capable of operating in conjunction with the plurality of fiber ports. Furthermore, this wavelength selective switch has a dispersive element and a switching element. The dispersive element decomposes at least one optical signal into a plurality of wavelength components. The switching element is composed of MEMS (Micro Electro Mechanical System) mirrors and configured to guide one selected from the plurality of wavelength components to one selected from the plurality of fiber ports. Patent Literature 2 (Japanese Translation of PCT Application Publication No. 2010-509639) discloses an optical switch. This optical switch has two fiber port arrays each of which has a plurality of fiber ports. Each fiber port array is configured either with N input fiber ports and 1 output fiber port or with 1 input fiber port and N output fiber ports. Light beams input from the two respective fiber port arrays are guided to two respective MEMS mirrors by a beam guide element disposed immediately in front of a switching element.